1. Field of the Invention
The present invention relates to a content transmission system, transmission server, communication terminal, and content transmission method that handle such digital content as copyright protected images, music, and videos.
2. Related Background Art
Recently, fee-based digital content such as ring tones are being purchased using cellular phones and the like. Moreover, digital content such as images, music, and videos can be downloaded by communication terminals that can connect to a network. These contents are copyrighted, and technologies to protect the copyright of the content are well-known. For example, information to prevent duplication of content is embedded in the content file so that the content can only be used by the communication terminal that downloaded the content.
Moreover, cited in Japanese Patent Application Laid-open No. 2005-174132 is technology that, when data with an established copyright is included in the content that a user has designated for mail transmission to a communication terminal, the data with the established copyright is deleted and the mail message is transmitted.